Magnetic resonance imaging (MRI) is the method of choice for noninvasive diagnosis of soft tissue disease in humans, and has wide applications in cardiovascular diseases. For example, contrast enhanced magnetic resonance angiography (CE-MRA) allows a high resolution three dimensional depiction of the vasculature. However, in the thorax, image quality may suffer from respiratory and cardiac motion and vascular pulsation, which have the potential to cause major ghosting and blurring artifacts, thereby limiting the clinical usefulness of this technique.
Respiratory motion is counteracted by instructing patients to hold their breath. Suppressing vascular pulsation artifacts relies on ECG (electrocardiogram) triggering or gating. Restricting data acquisition to a cardiac phase specific window has been proposed for time-of-flight magnetic resonance angiography (TOF-MRA) in the lower extremities and for phase contrast magnetic resonance angiography (PC-MRA) of carotid artery disease. Systolic (maximizing inflow) or diastolic (minimizing motion) cardiac phases are used as acquisition windows when data acquisition is restricted to a cardiac phase specific window. To reduce the unavoidable lengthening of scan times, gating is restricted to views within a certain region in k-space, mostly the central part of the k-space.
The use of ECG triggering or gating has also been extended to contrast enhanced MRA. Typically, for a Cartesian acquisition matrix, all phase encodings for a fixed slice encoding are acquired in a single window within one cardiac interval using linear view ordering, which limits the possible number of phase encodings. The central slice encodings are acquired halfway through the scan. This technique has been used to evaluate coronary artery bypass graft patency and thoracic abnormalities. However, because these techniques use only a portion of the cardiac cycle, they increase scan time and do not make maximum use of the contrast bolus.